I've put up the first attempt at a ballpark importer at
http://www.bourtonville.co.uk/OOTPStadium.zip
Unzip the file and then double click the OOTP Stadium Importer.application to install it.
How this works is as follows:
1. Start the program and exit OOTP
2. Choose your saved league directory by clicking on the ... next to the Saved Game Dir text box and navigating to it.
3. On the first go through only the top button will be enabled as there isn't an import file made at that point. Click on create new format CSV and when the other button has become enabled it has finished the first stage.
4. If you look in your saved league directory you will see a file called parks_output.csv - open this up in Excel or any other spreadsheet and you'll see the main parts of stadium data. Each park will have its teams listed against it as well. Make the changes to the data that you want and save it back as csv with the same name 'parks_output.csv'
5. Click the Import Ballparks button and it will read the file back in and update teams.dat and parks.dat
Points to note
a. It doesn't allow addition or deletion of stadiums.
b. If a team is allocated to more than one stadium, they'll be allocated the last one in the list.
c. If a team is mispelled in the list it won't get allocated its rightful stadium.
d. A ballpark can have up to five teams that play there.
e. A back-up of both teams and parks.dat are created so if it screws up you can delete teams.dat and parks.dat and rename the last backup copy.
I know it's not the same format as Gambo's list but I was trying to find someway of tying up a park to a team as well.